The present invention relates to glass melting and more particularly to a method of refining molten glass. The invention also relates to improved apparatus for use in refining molten glass.
In a known method of manufacturing glass in a continuous process, raw materials are fed in at one end of a glass melting tank to form a blanket floating on an existing bath of molten glass. The rate of feeding is sufficient to maintain a constant glass depth in the tank whilst molten glass progressively flows towards the opposite end of the tank known as the working end, from which molten glass is taken away for use in a forming process. The blanket of raw materials is converted to molten glass as it passes through a melting zone at one end of the tank by heat which may come for example from burning fuel supplied from burners situated at spaced intervals in the side walls above the glass level or from electrical heating devices. The molten glass passes from the melting zone into a refining zone where heat is also applied above the molten glass. In the refining zone bubbles of gas still remaining in the glass are encouraged to escape or go into solution in the glass. The glass passes from the refining zone into a conditioning zone adjacent the working end of the tank. In the conditioning zone the glass is homogenised and brought to a suitable thermal condition for use in the forming process. Normally a canal leads from the working end of the tank to a forming process.
To obtain glass free from gas bubbles and refractory corrosion products and to extend the life of the glass melting tank it is desirable to ensure that the glass in contact with the refractory is sufficiently cold. This is in part achieved by the convection flows set up in the molten glass within the tank, the flows causing glass to return from the colder to hotter areas in the lower sections of the tank. This can involve four or more times as much glass returning in the return flow within the tank as is being supplied to the forming process in the upper forward moving layers of molten glass. In this way additional heat is required to bring the return flowing glass to the temperature required in the forward flow.